/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/************************************************************************
 * libc/misc/lib_sendfile.c
 *
 *   Copyright (C) 2007, 2009, 2011, 2013 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ************************************************************************/

/************************************************************************
 * Included Files
 ************************************************************************/

#include <tinyara/config.h>

#include <sys/sendfile.h>
#include <stdbool.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

#include "lib_internal.h"

#if CONFIG_NSOCKET_DESCRIPTORS > 0 || CONFIG_NFILE_DESCRIPTORS > 0

/************************************************************************
 * Private types
 ************************************************************************/

/************************************************************************
 * Private Variables
 ************************************************************************/

/************************************************************************
 * Public Variables
 ************************************************************************/

/************************************************************************
 * Private Functions
 ************************************************************************/

/************************************************************************
 * Public Functions
 ************************************************************************/

/************************************************************************
 * Name: sendfile / lib_sendfile
 *
 * Description:
 *   sendfile() copies data between one file descriptor and another.
 *   sendfile() basically just wraps a sequence of reads() and writes()
 *   to perform a copy.  It serves a purpose in systems where there is
 *   a penalty for copies to between user and kernal space, but really
 *   nothing in TinyAra but provide some Linux compatible (and adding
 *   another 'almost standard' interface).
 *
 *   NOTE: This interface is *not* specified in POSIX.1-2001, or other
 *   standards.  The implementation here is very similar to the Linux
 *   sendfile interface.  Other UNIX systems implement sendfile() with
 *   different semantics and prototypes.  sendfile() should not be used
 *   in portable programs.
 *
 * Input Parmeters:
 *   infd   - A file (or socket) descriptor opened for reading
 *   outfd  - A descriptor opened for writing.
 *   offset - If 'offset' is not NULL, then it points to a variable
 *            holding the file offset from which sendfile() will start
 *            reading data from 'infd'.  When sendfile() returns, this
 *            variable will be set to the offset of the byte following
 *            the last byte that was read.  If 'offset' is not NULL,
 *            then sendfile() does not modify the current file offset of
 *            'infd'; otherwise the current file offset is adjusted to
 *            reflect the number of bytes read from 'infd.'
 *
 *            If 'offset' is NULL, then data will be read from 'infd'
 *            starting at the current file offset, and the file offset
 *            will be updated by the call.
 *   count -  The number of bytes to copy between the file descriptors.
 *
 * Returned Value:
 *   If the transfer was successful, the number of bytes written to outfd is
 *   returned.  On error, -1 is returned, and errno is set appropriately.
 *   There error values are those returned by read() or write() plus:
 *
 *   EINVAL - Bad input parameters.
 *   ENOMEM - Could not allocated an I/O buffer
 *
 ************************************************************************/

ssize_t sendfile(int outfd, int infd, off_t *offset, size_t count)
{
	FAR uint8_t *iobuffer;
	FAR uint8_t *wrbuffer;
	off_t startpos = 0;
	ssize_t nbytesread;
	ssize_t nbyteswritten;
	ssize_t ntransferred;
	bool endxfr;

	/* Get the current file position. */

	if (offset) {
		/* Use lseek to get the current file position */

		startpos = lseek(infd, 0, SEEK_CUR);
		if (startpos == (off_t)-1) {
			return ERROR;
		}

		/* Use lseek again to set the new file position */

		if (lseek(infd, *offset, SEEK_SET) == (off_t)-1) {
			return ERROR;
		}
	}

	/* Allocate an I/O buffer */

	iobuffer = (FAR void *)lib_malloc(CONFIG_LIB_SENDFILE_BUFSIZE);
	if (!iobuffer) {
		set_errno(ENOMEM);
		return ERROR;
	}

	/* Now transfer 'count' bytes from the infd to the outfd */

	for (ntransferred = 0, endxfr = false; ntransferred < count && !endxfr;) {
		/* Loop until the read side of the transfer comes to some conclusion */

		do {
			/* Read a buffer of data from the infd */

			nbytesread = read(infd, iobuffer, CONFIG_LIB_SENDFILE_BUFSIZE);

			/* Check for end of file */

			if (nbytesread == 0) {
				/* End of file.  Break out and return current number of bytes
				 * transferred.
				 */

				endxfr = true;
				break;
			}

			/* Check for a read ERROR.  EINTR is a special case.  This function
			 * should break out and return an error if EINTR is returned and
			 * no data has been transferred.  But what should it do if some
			 * data has been transferred?  I suppose just continue?
			 */

			else if (nbytesread < 0) {
				/* EINTR is not an error (but will still stop the copy) */

#ifndef CONFIG_DISABLE_SIGNALS
				if (errno != EINTR || ntransferred == 0)
#endif
				{
					/* Read error.  Break out and return the error condition. */

					ntransferred = ERROR;
					endxfr = true;
					break;
				}
			}
		} while (nbytesread < 0);

		/* Was anything read? */

		if (!endxfr) {
			/* Yes.. Loop until the read side of the transfer comes to some
			 * conclusion.
			 */

			wrbuffer = iobuffer;
			do {
				/* Write the buffer of data to the outfd */

				nbyteswritten = write(outfd, wrbuffer, nbytesread);

				/* Check for a complete (or parial) write.  write() should not
				 * return zero.
				 */

				if (nbyteswritten >= 0) {
					/* Advance the buffer pointer and decrement the number of bytes
					 * remaining in the iobuffer.  Typically, nbytesread will now
					 * be zero.
					 */

					wrbuffer += nbyteswritten;
					nbytesread -= nbyteswritten;

					/* Increment the total number of bytes successfully transferred. */

					ntransferred += nbyteswritten;
				}

				/* Otherwise an error occurred */

				else {
					/* Check for a read ERROR.  EINTR is a special case.  This
					 * function should break out and return an error if EINTR
					 * is returned and no data has been transferred.  But what
					 * should it do if some data has been transferred?  I
					 * suppose just continue?
					 */

#ifndef CONFIG_DISABLE_SIGNALS
					if (errno != EINTR || ntransferred == 0)
#endif
					{
						/* Write error.  Break out and return the error condition */

						ntransferred = ERROR;
						endxfr = true;
						break;
					}
				}
			} while (nbytesread > 0);
		}
	}

	/* Release the I/O buffer */

	lib_free(iobuffer);

	/* Return the current file position */

	if (offset) {
		/* Use lseek to get the current file position */

		off_t curpos = lseek(infd, 0, SEEK_CUR);
		if (curpos == (off_t)-1) {
			return ERROR;
		}

		/* Return the current file position */

		*offset = curpos;

		/* Use lseek again to restore the original file position */

		if (lseek(infd, startpos, SEEK_SET) == (off_t)-1) {
			return ERROR;
		}
	}

	/* Finally return the number of bytes actually transferred (or ERROR
	 * if any failure occurred).
	 */

	return ntransferred;
}

#endif							/* CONFIG_NSOCKET_DESCRIPTORS > 0 || CONFIG_NFILE_DESCRIPTORS > 0 */
